| Year | Value | | 2020 | 0.10337424297211 | | 2019 | 0.12740787707547 | | 2018 | 0.13125658058926 | | 2017 | 0.13435868468593 | | 2016 | 0.13864382045196 | | 2015 | 0.143077300683 | | 2014 | 0.1475784057191 | | 2013 | 0.15229534998335 | | 2012 | 0.157213150021 | | 2011 | 0.16232964800406 | | 2010 | 0.16779639198574 | | 2009 | 0.17341208099797 | | 2008 | 0.17862041720063 | | 2007 | 0.18474859570363 | | 2005 | 0.19799433108093 | | 2004 | 0.20530736530262 | | 2003 | 0.21387253711258 | | 2002 | 0.22436986410513 | | 2001 | 0.23330572548915 | | 2000 | 0.22452964959424 | | 1999 | 0.25042931045233 | | 1998 | 0.25902059169351 | | 1997 | 0.26751894047841 | | 1996 | 0.27629714887837 | | 1995 | 0.28535689156438 | | 1994 | 0.22226952746408 | | 1993 | 0.25085919273512 | | 1992 | 0.2595780515509 | | 1991 | 0.22398811967013 |
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